Dry kiln and in the art of kiln drying



July 2, 1935.

J. F. COBB DRY KILN AND IN THE ART OF KILN DRYING Filed Oct. 29, 1930 '7 Sheets-Sheet 1 I 34 3/ 4d E3? 5 4/ 44 4/ 44 4/ 4 44 IZJ 4 4/ 4 13/ its y 1935- J. F. COBB DRY KILN AND IN THE ART OF KILN DRYING Filed Oct. 29, 1930 '7 Sheets-Sheet 2 duo: wag I I July 2, 1935. J. F. COBB DRY KILN AND IN THE ART OF KILN DRYING Filed Oct. 29, 1930 '7 Sheets-Sheet 3 5 m. fihml l w Mfi w, m w! R m w V n i 1 t4! n41 n u .v SQ QWID \km. $19 NW N m M \MCWIWNY P r July 2, 1935. c 2,006,670

DRY KILN AND IN THE ART OF KILN DRYING Filed Oct. 29, 1930 7 Sheets-Sheet 4 32 LY fl 'akfl 212 39 2 E z/ L 27 /4 1 '15 N 27 fi I l gin minimal '7 Sheets-Sheet 5 J. F. COBB Filed Oct. 29.

DRY KILN AND IN THE ART OF KILN DRYING FM Mm July 2, 1935.

July 2, 1935. J. F. COBB DRY KILN AND IN THE ART OF KILN DRYING 1930 7 Sheets-Sheet 6 F1 Led Oct. 29,

PM mrm JulyZ, 1935. J. F. COBB 2,006,670

DRY KILN AND IN THE ART OF KILN DRYING Filed Oct. 29., 1930 7 Sheets-Sheet 7 XIX Fig. m

Fug. XIX:

C/g %WM JIZYENTOR:

fig; in/M ATTORNEY- Patented July 2, 1935 PATENT OFFICE DRY KILN AND IN THE ART OF KILN DRYING James Forrest Cobb, Portland, Oreg.

Application October 29,

21 Claims.

My invention relates to improvements in the art of kiln drying and in dry kilns, and particularly in the distribution systems thereof where the circulating system, heating system, ventilating system, and humidifying system, respectively, are distributed throughout the length of the kiln, and where it is essential that the heat and humidity be equally distributed as in charge or compartment kilns.

One object of my invention is to permit multiple heat control in a simple manner consistent with producing uniform heating conditions throughout the length of the kiln.

Another object of my invention is to produce substantially uniform heat and humidity distribution and, consequently, uniform drying effect throughout the length of the kiln.

Another object of my invention is attained by the manner of positioning and distributing the heating coils within the kiln in relation to the circulating system.

Another object of my invention is the producing of a directed circulation to give equal heat and humidity conditions throughout the length of the kiln.

Besides the objects specified, my invention includes the production of certain improved means which contribute to the attaining of more uniform drying results. 7

The embodiment of my invention relating in part to overhead fans is claimed in my co-pending application, Serial No. 24,655, filed June 3, 1935, which is a continuation in part of my present invention.

What constitutes my invention will be hereinafter specified in detail and succintly set forth in the appended claims.

Figure I is a longitudinal vertical section of one form of embodiment of my invention showing my heating system and circulating system within the kiln, with fan ducts removed.

Figure II is a plan view of the same but showing the fan duct and heating systems in place within the kiln.

Figure III is a transverse vertical section at III-III of Figure I of my invention showing the fan duct and. heating systems in place.

Figure IV is a transverse vertical section at the line IV-IV of Figure I.

Figure V illustrates a modified form of fan ducts having baiiles located within the fan ducts instead of on the corners of the fan duct wall.

Figure VI is a plan view of a modified form of embodiment of my invention furnished with all right hand fans.

1930, Serial No. 492,026

Figure VII is a longitudinal vertical section of a modified form of my kiln having all right hand fans located above the stock-loads.

Figure VIII is a transverse longitudinal section of a part of my kiln illustrating a modified form 5 of heating system inoperative relationship to the fans, with fan ducts removed.

Figure IX is a similar view of another modification of my invention in respect to the heating system in relation to the fans.

Figure X is a similar view of my kiln illustrating another modified form of heating system, with fan ducts removed.

Figure XI illustrates diagrammatically a preferred form of embodiment of my heating systems. 15

Figure XII is a plan view of a modified form of my invention showing fans above the stock-loads and in one corner of the kiln.

Figure XIII is a vertical longitudinal section taken through the fan ducts illustrated in Figure 20 XII.

Figure XIV illustrates a transverse vertical section XIV-XIV of Figure XII.

Figure XV illustrates a transverse vertical section at XV-XV of Figure VI.

Figure XVI is a detail illustration of 9. diaphragm valve detached.

Figure XVII is a cross section of one of my spray nipples illustrated in Figure I, III and IV.

Figure XVIII is a view similar to that of Figur II except illustrating amplified surface radiatlo and fans of increased capacity at the ends of the kiln.

Figure XIX is a longitudinal vertical section of my kiln as taken on the line XIX-XIX of Figure XVIII.

Referring to the numerals on the drawings, in each figure thereof Wherethey appear, I indicates opposite side walls of the kiln, 2 the fioor, 3 the roof, and 4 the end walls defining a closed chamber and constituting the outside walls of the kiln. Said walls may be of any suitable and preferred material and construction, and are combined in any manner preferred so as to confine within the closed chamber or kiln the gaseous circulatory medium with the heat that is imparted to it.

The end walls 4, or at least one of them, are preferably made to include some form of door by which material to be dried may be conveniently introduced into the kiln and withdrawn from it.

Extending lengthwise through the kiln are tracks or rails 5 which are supported at suitable intervals within the kiln at desired elevation above the floor 2 as by cross-beams 6. The tracks are designed to support and carry wheeled trucks I, which may be of any usual form preferred, and which are united in pairs, preferably by crossbeams or bunks 8 on which the lumber or other material to be dried is piled in the usual manner.

Suspended from the cross-beams 6 are suitable hangers which are preferred as means of support for the pipe carrying member. Separating the heating pipes are the pipe spacers which hold the pipes separated so as to permit a free air flow across them.

The heating systems preferably consist of four return pipe systems, as shown for example in Figure II, the legs of each of which are joined in units at top and bottom by the headers l3, ll, l5, and I6, which are supplied with steam from a source of supply not illustrated, as by means of supply pipes II which are controllable as by automatic or hand control valves.

Each of the heating systems A and B consists of return pipes having two legs, one above the other, the upper one 2| leading from the top header I 3 at one end of the kiln, and the lower one 22 leading into the bottom header l6 at the same end of the kiln.

For convenience of identification, the header end of the kiln, in Figure I for example, will be designated upper end and the opposite end of the kiln will be designated lower end".

At the lower end of the kiln, the two legs 2| and 22 of the heating system B are joined by a return bend 25, and the two legs of the heating system A are joined with like effect at the lower end of the kiln by Us 21 and a nipple 28. The US 21 and the nipples 28 are used to permit the outer pipes 2| and 22 of the heating system A to lie in substantial parallelism and uniform proximity on the outside of the pipes of the inner system B on both legs of each system.

The pipes of the heating system, whether one or more, are located on each side of the kiln as illustrated or at suitable intervals, in case of a multiple track kiln which is contemplated by my invention. The entire heating system is, in all instances, installed so that its steam condensation will drain by gravity, as, for example, from the top headers I3 and I4, to the bottom headers I5 and I6, through the return fittings at the opposite end of the heating system designated return joint end for convenience.

It is well known in the art that uniform distribution of heat and humidity throughout the length of the kiln is essential in a charge kiln and that one of the functions of circulation is to distribute uniformly heat and humidity conditions throughout the length of the kiln. I accomplish this by the arrangement of my fan duct, heating and humidifying systems.

In the past, heating systems in internal fan kilns have not been designed with special consideration of the rapid condensation rate of steam within the heating pipes and the rapid loss in heating capacity of the steam as it travels within the pipes from one end of the heating system to the other. Consequently, the end of the kiln at which the steam enters has been the hottest end, which is an objectionable condition.

The use of thermostatic temperature control bulbs, of which one is indicated at 65 in Figure I, well known and commonly used in kilns, usu-' ally located at the same end of the kiln at which the steam enters the heating system, aggravates this condition by automatically cutting off the steam supply to the heating system when the temperature at the bulb reaches the set point. The fast circulation produced by the fan system, in rapidly recirculating the kiln atmosphere quickly conveys the heat from the pipes soon after the steam is turned on, to the temperature control bulb. In many cases, when very little steam is required to maintain the set temperature, the automatic control equipment frequently turns the steam on and then off the heating system before the steam can pass to the opposite end of the kiln from which it enters. Consequently, the upper end of the kiln is hotter than the lower end.

I overcome this objection by using a heating system of single or multiple units having, respectively, a single return, so that the bottom headers I5 and I6 are located at the sameend of the kiln as the top headers I3 and I4, and by providing sufficient slope in the pipes to permit water of condensation to drain by gravity from the top to the'bottom headers. This provides a space between the upper and lower legs of the heating system or systems at the steam feed or upper end of the kiln and provides very little space between the two legs of each system at the opposite or lower end of the kiln. By positioning the fans on the shaft (see Figures I, VIIIJCI), so that they are below the level of the top leg of the heating system, I am able to circulate substantially all the air through the top leg of the heating system at the upper or header end of the kiln and a portion only of the air through the bottom leg of the heating system at said end of the kiln. At the lower end of the kiln, on the contrary, agreater amount or substantially all the air or circulating medium will be passed through both legs of the heating system because the pipes at this end are located in the path of the circulating atmosphere.

By dividing the heating system into multiple units, two units on each side as illustrated in Figure III, and by reducing the amount of heating surface within the kiln to a practical minimum, the steam when turned on will pass from end to end of one system before the temperature within the kiln is raised to the set point, indicated by the thermostatic temperature control bulbs, aforesaid.

For producing kiln atmospheric circulation, I prefer'to use substantially such means as are commonly known as the internal fan cross circulation system. In such a system a series of reversible rotary fans 3| are mounted, preferably, on a common shaft 32 which rotates as in sleeve bearings 34 supported by the floor 3 of the kiln on bearing stands 36. In the case that overhead fans are employed, suitable supports 36 on beams 31 may be used. Cross circulation is preferably produced by means of a zigzag wall, extending substantially from end to end of the kiln as shown in Figure II.

The zigzag effect of said wall is achieved by dividing the length of the kiln into medial compartments, by a series of alternately disposed substantially parallel partition walls 39 and 40, each of the walls 38 being solid, for example only, of equivalent construction known in the art, and each of the walls 40 being provided with an aperture of suitable dimensions to accommodate within it one of a series of rotary fans 3|. Each pair of walls 39 and 40 that are next adjacent to each other is united on one side by a solid vertical wall 4| constituting in effect a closure on that side for the compartment to which it is appropriated, the side of the compartment opposite each solid wall being open.

The solid walls 4| when employed are disposed respectively in succession on alternate sides of the fan duct so as to divide the series of compartments into units or fan ducts of which each alternate one is open on one side and closed on the other side. By the disposition just described of the several walls 39, 40, and 4|, the result is, in their assemblage, to impart to the wall so constituted throughout its entire length what is designated as a zigzag direction or effect.

The angle at which the walls 39 meet the walls 4|, as shown in Figures II, IV, and VI, is an obtuse angle on the fan side, but it is obvious that the angle may be varied, if desired, as in some instances it may be (see for example Figures XII and XIII). Each of the walls last named is planted on the bottom 2 of the kiln or is, if overhead fans are used, in contact with airtight closure means assembled on their upper side with the ceiling or roof 3. The fan ducts are completed by a floor 42 which is laid in contact with air tight closure on the top of the walls 39, 40, and 4|, when the fans are below the loads, and are attached to the bottom of said walls in like manner when the fans are above the stock-loads.

I prefer to use a series of right hand fans at one end of the kiln and a series of left hand fans at the opposite end, the zig zag wall being reversed in direction at a medial portion of the kiln as shown in Figure II to provide cross circulation from one side to the other the full length of the kiln in which case in the intermediate compartment where right and left hand fans face each other, two fans will blow against each other'in counter-acting currents in one direction of circulation and withdraw atmosphere from the same compartment in the reverse direction of circulation as shown in Figure II.

The employment of right and left hand fans opposed in pairs distributed the full length of the kiln so that each pair of fans may discharge counteracting currents one against the other in either direction of rotation affords a feasable method of circulation, and can be used to embody my invention.

In any embodiment of my invention, I provide means for effecting more circulation of air in the end sections of the kiln which would otherwise be its coolest sections. This may be accomplished by the use of simple baffles as illustrated in Figures II, III, V, VI and XII or using large capacity fans in the end section of the kiln.

Referring to Figure III, I show bailles 44 and 45, the baflles 44 being relatively narrower than the baffles 45 because the latter must be prepotent and wide enough to reverse the circulatory currents and direct them towards the ends of the kiln when the fan circulation is directed against, them. On reversal of circulation, the baffles 44 would be brought into effective use.- They need be relatively narrower than the bailles 45 because the air from the fans being in such case directly driven towards the ends of the kiln, their function is accomplished by directing the air partially transversely and, at the same time, allowing a certain amount of directional flow towards the ends, due to the direct action of the fans.

Upon reversal of the fans the transverse air circulation of the kiln is reversed and the longitudinal circuit of air circulation at each end is also reversed. Each circuit of longitudinal air circulation moves from the center portion of the kiln towards one of the two ends in one direction of fan rotation, and upon reversal of fan rotation each longitudinal circuit is reversed and moves toward one end from the middle portion of the kiln on the opposite side of the stock loads from the side on which it moved, before the fans were reversed.

It will be understood that the baffles 44 and 45 are preferably set with permanent flexure so that they may be made by adjustment to direct as much additional movement of atmosphere towards the ends of the kiln as may be effective to prevent those ends from becoming tOo low in temperature and too high in humidity. On the contrary, it is made possible, upon occasion, to reduce the temperature and raise the humidity at the ends of the kiln by reducing the air flow towards the ends of the kiln or by reducing the amount of circulation at the end of the kiln.

Referring to Figure II, it will be noted that the bailles 45 are all disposed on the same side of the kiln, whereas the bafiles 45 are-located in series on opposite sides of the kiln as shown in Figure VI.

In Figures XII, XIII and XIV, the bailles 44 and 45 are shown as located on adjacent sides only of the fans, inasmuch as thefans are located in one corner of the kiln which design is also contemplated as one form of embodiment of my invention.

By my invention, however, I propose to use such width of battles as may be, by adjustment, made effective in directing air circulation towards what would be without this the coolest parts of the kiln.

When the fans are revolving in one direction for instance, clockwisethey blow toward one side of the kiln and suck from another side. The duct walls may be provided with wing baffles 44 and 45 which are preferably made of metal and are preferably adjustable by permanent flexure to guide and distribute the impinging circulating medium within the kiln.

It has been noted that the wing bailles 44 are comparatively narrow and the wing baffles 45 wider. It is desired to set these wing baffles so that the air of circulation from the fans 3| will be mainly transverse in course but will have a slight directional flow toward the respective ends of the kiln where I prefer to direct additional heated air from the fans 3| to replace cooler air at the doors where it has lost heat. This directional air flow sets up longitudinal recirculation toward the doors from the medial portion of the kiln on one side thereof and toward the part of the kiln remote from the doors on the opposite side of the kiln.

It is to be understood that the fans may be located above as well as below the stock-loads of material to be dried. In this case, the relative disposition of the heating system to the fans already described above, is maintained. In some cases the fans may be located in one corner of the kiln, as shown in Figure XIV, in that case the heating system would be in two multiple units of pipes instead of four as illustrated in Figure III.

In single ended kilns, or those having doors at one end only, I prefer to circulate at or direct more air toward the door than toward the blank end, because of the greater heat loss occasioned by leakage of air at thedoor.

The wing baffles 44 and 45 may be of any preferred size, shape or available disposition. Their primary function being to direct the air from the fans to the normally cooler parts of the kiln, they may be located at the comers of the ducts in Figure II, or midwise of the duct, as in Figure V or they may be omitted altogether when right and left hand fans are used in series at'opposite ends of the kiln as illustrated in Figure XVIII.

If the fans are located in one corner of the kiln, as they may be, the wing baflles will be on adjacent sides of the series of fan housings, as illustrated in Figures XII and XIII and XIV. In these cases, the. functions of the baflies are the same as in Figures I and II.

In my kiln, I prefer to provide fresh air con-- duits 46 and 41 having openings 49 and 50 respectively ateach fan for the intake of outside or atmospheric air into the kiln. In the case of overhead fans, ventilators maybe substituted for said conduits, and will perform the double purpose of fresh air intake and exhaust from the kiln.

{The fresh air conduits 46 and 41 are provided, respectively, with fresh air doors 52 and 53, which may be opened at will to let fresh air into the respective conduits 46 and 41. The air conduits may have openings 49 and 50 provided with covers 56. Said covers are preferably sliding doors and can be used, respectively, to cover all or part of the openings 49 and 50 so that the fresh air intake at each fan is adjustable in such manner as to provide a desired modicum of fresh air to each fan. Preferably only, one fresh air conduit 46 or 41 will be used at a time. The one on the suction side of the fans will be used and the door 52 or 53 of the opposite side will be closed, depending upon the direction of circulation of the fans, considering that the fans are reversible. I also provide ventilators 51 in the roof of the kiln which may be opened at will to ventilate excess moisture from the kiln.

Attention is next directed to the arrangement of the humidifying sprays. One spray pipe 58 is preferably provided within the kiln withnippics 60 each of which is transversely perforated near its end by small holes BI and is covered with a cap 62, so as to cause it to spray in opposite directions; that is, toward opposite ends of the kiln in such a way that the discharge from the holes will humidify the air and distribute it equally, whatever be the direction of circulation.

Attention is called to the direction at which the spray pipe nipples 60 point in Figure I. They are shown as directed slightly upwardly at an angle of substantially 45 at the upper and lower ends of the kiln, whereas, in the middle, they are shown as pointing downwardly substantially at an angle of 45. This arrangement permits the condensed moisture within the spray pipe to be discharged in the middle of the kiln which is usually the highest in temperature and lowest in humidity and where thismoisture will do most towards equalizing humidity distribution within the kiln. It is understood that the upward or downward direction of the spray nipples 60 may be changed at will to distribute the moisture to the lowest humidity points if variation should occur due to abnormal conditions.

There are several modifications of my heating system illustrated in Figures VIII, IX, and X, which give the same relationship of eifective radiating surface to air circulation as that shown in Figure I. In all these illustrations, part of the air circulated is permitted to bypass part of the heating units of the heating system at the upper ends of the system at which the steam enters, and at the lower end or return leg end of the system or substantially greater volume of the air is passed in operative communication with the heating system.

In Figures VIII, IX, X and XI the heating systems illustrated are on one side of the fan system. In these figures the fan ducts are removed and it is to be understood that the heating systems illustrated preferably are to be used on the opposite sides of the fans and fan ducts from the heating systems illustrated in these figures.

The amount of air bypassing the heating. units varies in different cross sections of the kiln; but the closer to the point of feeding steam, the relatively greater the amount of air that is bypassed; and the closer to the return leg ends of the heating'system, the greater the volume of kiln atmosphere that is circulated across the pipes. This relationship of volume of air passing across the pipes to the heating efliciency of the pipes is maintained. The numerals of Fig. XI are applicable to Figs. VIII, IX, and X.

In some cases I provide extended surface radiation on the coils at the ends of the kiln.

perature control, well-known in the art, is set for V a given schedule of temperature and humidity. Steam is supplied to one of the heating systems A which is of sufficient radiating surface to permit a rapid flow of steam from the top to the bottom header. The rapid circulation cooled by drying contact with the stock to be dried and then passing across the pipes condenses a considerable amount of steam in them so that the steam in each pipe loses heating capacity as the steam moves from the-top to the bottonheader. As a consequence, the relative heating capacity of each system at the upper end is greater than at the return bend or lower end. Compensation by rel-- of the circulating medium across all the pipes at the lower end than through that part of the system which is located at the upper end of the kiln. A greater uniformity of the heating of the kiln results.

The bafiles when used are set so as to deflect the greater amount of circulation towards the ends of the kiln or regions which are naturally relatively cooler and higher in humidity, due to heat losses as through the doors. By adjusting the bafiies in the manner already indicated, a more uniform distribution of heat and humidity can be obtained. A similarly adjustment of the direction of the spray nipples produces a uniform distribution of humidity. It is largely by the control of the drainage in each of the heating coils and adjustment of the directional flow of the circulating medium, and the adjustment of the direction of the spray nipples, that I am able to produce more uniform heat and humidity distribution within the kiln and better drying of the stock.

In some cases a heating system having steam feed headers at one region of the kiln and drain headers at another region of the kiln may be used. In such case, it would be necessary to use compensating factors to increase the radiation at the lower end of the kiln. This may be accomplished by using greater surface radiation, such as additional or fin pipe at the lower end to compensate for the less effectiveness of the heating system at that region. Compensation could also be made for less radiation at any point in the kiln by use of larger fans or of fans having a greater angle of blade which would permit them to discharge more air through the stock loads and across the heating system at the end sections of the kiln or other sections where the capacity of the drying atmosphere may be less. In fact, extended surface radiation, the use of larger fans, or fans having a greater angle of blades may be used at any points in the kiln to raise temperature or to increase the drying effect of the circulating atmosphere in lieu of the arrangement described above.

The principle of my invention contemplating means for compensating for greater heat and humidity losses at the ends of a kiln, for example, may be employed in kilns having distributed fans operatively mounted on transverse shafts as well as on longitudinal shafts. In any case, greater heating surface at the ends of the kiln, adjustment of humidity spray discharge pipes to supply drier steam'at the ends of the kiln and wetter steam in the intermediate section, or the use of larger fans or fans having a greater angle of blade to circulate a greater volumeof air at the ends of the kiln, may be used to accomplish the desired result. I prefer to employ any or all of these means operating individually or simultaneously to provide more uniform drying-conditions within the kiln.

When fans on transverse shafts are used, I prefer to use right hand fans at one end and left hand fans at the opposite end of the kiln, installed so that the effective direction of discharge of right hand fans will be toward the end of the kiln at which they are located, and the effective direction of the left hand fans will be toward their end of the kiln. In this manner greater heating effect is attained at the ends of the kiln, or whatever cooler regions thereof may exist, towards which they may be respectively made to discharge.

What I claim is:

l. The method of drying stock in a charge kiln which consists in effecting transverse circulation of heated air therein, and in effecting a greater volume of transverse air circulation, a greater amount of heat and a drier vapor spray at the two ends of a kiln than in the intermediate region thereof.

2. In a dry kiln, the combination of a distributed air circulating system, a distributed humidifying system, a distributed heating system, each extending substantially the full length of the kiln, and means in two of said systems for supplying a greater amount of heat at the ends than at the medial portion of the kiln.

3. In a dry kiln having a series of fans operatively mounted and distributed in substantial alignment therein, the combination of a return coil heating system comprising top and bottom headers, and top and bottom legs connected, respectively, thereto, said headers being vertically spaced apart at one end of said heating system, said legs converging and being connected by a return joint at its opposite end, said headers being supplied with steam and drained respectively, said heating system being so related to said fans that a greater volume of air is circulated across the upper leg than across the lower leg of said heating system, and a greater being connected to volume of air is circulated across the return joint end of said bottom leg than across the header end thereof.

4. In a dry kiln having a series of fans operatively mounted and distributed in substantial alignment therein substantially the full length of said kiln, the combination of a heating system distributed adjacent to said fans and having top and bottom headers at one end of said kiln and top and bottom legs connected, respectively, thereto, said headers being vertically spaced apart at one end of said heating system and being connected by a return joint at its 0pposite end, said headers being supplied with steam and drained respectively, the supply header being at a level higher than the return joint end and than theaxis of the fans, and the bot tom header being at a level lower than the return joint end and than the axis of the fans, whereby the air from the fans at the return joint end of said heating system is made to pass across both legs, more of the air from the fans at the header end of said heating system passing across the top leg than across the bottom leg.

5. In a dry kiln, the combination of a series of fans operatively mounted and distributed in substantial alignment therein substantially the full length of the kiln, a return coil heating system distributed therein adjacent to said fans and comprising top and bottom legs, the top leg having a supply header end at a higher elevation than the axis of the adjacent fans at one end of the kiln, and a return joint end, said bottom leg having a return joint end and a drain header end at a lower elevation than the axis of adjacent fans at the other end of the kiln, said heating system having drainage from said top to said bottom header, said fan system being so related to said heating system that the fans at the header ends of said heating system circulate more air across the header end of the top leg and less air across the header end of the bottom leg, and the fans at the return joint end circulate substantially all the air across the return joint ends of both legs, whereby more uniform heat distribution is effected within the kiln.

6. In a kiln, the combinationof an overhead air circulating system located beneath the kiln roof, a wall beneath said roof dividing the space therebeneath into a series of differently facing compartments, said air circulating system comprising a plurality of right and left hand fans operatively mounted at intervals in series in openings provided in said wall at opposite ends, respectively, of the kiln, and a return coil heating system comprising upper and lower legs mounted in operative communication with said air circulating system, said upper and lower legs top and bottom steam headers respectively, said top header being higher than the horizontal axis of said fans, and said bottom header being lower than the horizontal axis of said fans, whereby a greater volume of air circulation is effected across a lower than an upper leg of said heating system and a greater volume of air circulation is effected across one end of said top leg than across the opposite end.

7. In a dry kiln the combination, with a distributed air circulating system comprising fans operatively mounted therein, inner and outer return coil heating systems adjacent to said air circulating system substantially the full length of the kiln,-each heating system comprising supply and drain headers with upper and lower legs having supply and connected respectively thereto and being sloped for drainage, the supply headers being higher than, and the drain headers being lower than the longitudinal axis of adjacent fans, the inner coil being disposed between the legs of the outer coil, and the top and bottom headers of the inner and outer coils being respectively adjacent to each other, the inner return coil having a return bend at the end opposite the header end, and the outer return coil having a return connection on the outside of the return bend of the inner coil, providing a substantially uniform spacing between the coilsin the two systems, said heating systems being so related to said air circulating system that more atmosphere is circulated across the top legs of said heating systems than across the bottom legs.

8. In a dry kiln, the combination with an air circulating system therein distributed substantially its full length, two heating systems each disposed substantially the full length of the kiln, each in operative relationship to said air circulating system, said heating systems having supply and drain headers, the supply header of one heating system being steam fed at one end of the kiln, and the supply header of the other heating system being steam fed at the opposite end of the kiln whereby each fan circulates kiln atmosphere across relatively different portions of each of said heating systems simultaneously.

9. In a dry kiln, the combination with an air circulating system therein distributed substantially its full length, two heating systemseeach disposed substantially the full length of the kiln,

each in operative relationship to said air circulating system, each one of said heating systems drain headers at the same end of the kiln, the supply header of one heating system being steam fed at one end of the kiln and the supply header of the other heating system being steam fed at the opposite end of the kiln, said air circulating system comprising right and left hand fans whereby each right and left hand fan circulates atmosphere across relatively different portions of each heating system simul-. taneously.

10. In a dry kiln, the combination of an air circulating system, comprising a series of fans operatively mounted and distributed substantially the full length of the kiln, for circulating atmosphere substantially transversely therein, two return coil heating systems, one at each end of the kiln, disposed in operative relationship to different portions of said circulating system, each of said heating systems having a supply header spaced substantially vertically above a drain header, the corresponding portion of said heating systems being oppositely sloped for gravity drainage in opposite directions, whereby the circulation of kiln atmosphere across each of said heating systems provides substantially the same heating effect from the medial portion to its respective end of the kiln.

11. In a dry kiln, the combination of an air circulating system, comprising right and left hand fans operatively mounted in series at the two ends respectively, of the kiln, and fan ducts for directing movement of atmosphere transversely therein, two return coil heating systems, each having upper and lower legs extending substantially half the length of the kiln, the two systems in series extending substantially the full length of the kiln disposed in operative'relationship to said air circulating system, the upper and lower legs of each of said heating systems, respectively, being sloped for gravity-drainage of condensation therein in opposite directions.

12. A dry kiln comprising within it a fan duct defined in part by a continuous substantially vertical wall extending substantially the full length of the kiln in a zigzag direction, in combination with a plurality of fans mounted on a driven shaft, baffles of relatively different widths so disposed on opposite sides of said vertical wall respectively that the wider shall be located in the blast of a fan when discharging air toward the middle of the kiln, and the narrower bafile located in the blast of a fan when discharging air toward the adjacent end of the kiln, in either direction of fan rotation.

13. In a dry kiln, the combination of a series of distributed fans comprising an air circulating system, operatively mounted in an interior corner of the kiln, fan ducts for directing the kiln atmosphere transversely therein, a single return heating system having upper and lower legs operatively mounted on one side of said air circulating system, baffles disposed in operative communication with said fan ducts, wide baffles being disposed in the blast of each fan discharging air'toward the middle of the kiln and narrow baiiles disposed in the blast of each fan discharging toward the adjacent end of the kiln, the upper leg of said heating system extending higher than, and the lower leg, lower than the horizontal axis of said fans, whereby and more air passing across the upper than the lower of said legs, with the effect of promoting more uniform drying within the kiln.

14. In a dry kiln having a heating system and an air circulating system distributed substantially the full length of the kiln, a vapor spray mounted therein and extending substantially the full length of the kiln, said spray comprising a pipe operatively connected to a source of vapor supply, said pipe having a plurality of capped nipples extending laterally therefrom, transverse vapor discharge holes in said nipples, said nipples being directed upwardly at the ends-of the kiln and downwardly in the medial portion of the kiln.

15. In a dry kiln, the combination therewith of means for producing transverse circulation of heated atmosphere therein, of a vapor spray pipe operatively extending substantially horizontally the full length of said kiln, said spray pipe having an outlet above the horizontal axis thereof for discharging vapor therefrom at each of the ends of the kiln, and outlet below the horizontal axis of said pipe for discharging water and vapor therefrom in the middle portion of said kiln, whereby more vapor and less water is discharged at the ends than at the middle portion of the kiln.

16. In a dry kiln, the combination with a distributed air circulating means, a distributed heating system, a distributed substantially horizontal humidifying system, said systems being effective substantially the full length of the kiln, said humidifying system comprising a pipe having outlets above the horizontal axis of said pipe at the ends of the kiln and outlets below the horizontal axis of said pipe in the medial portion of the kiln, said circulating means and said heating system including means whereby more heat is released and circulated transversely therein at the ends than'at the medial portion of the kiln.

17. In a dry kiln having walls defining the same, the combination with a series of fans, fan ducts and baffles distributed substantially the full length of the kiln for efiecting two longitudinal circuits moving in opposite directions and transverse air circulation therein, a heating system extending substantially the full length of the kiln on one side in the path of circulation of said air circulating means, and extended heating surface on pipes of said heating system at each of the two ends of the kiln in the path of said transverse air circulation, the two end fans, one at each end of the kiln, having a greater air circulating capacity than the other fans whereby a greater amount of heat is released and circulated at the ends of the kiln than at an intermediate section thereof.

18. In a dry kiln having walls defining the same, the combination of a series of fans operatively mounted on a longitudinal shaft and distributed therein, a heating system extending substantially the full length of the kiln, on one side of said series of fans, means for distributing air circulation transversely across said heating system, the fans at the two ends of said series having a greater circulating capacity than intermediate fans, whereby a greater amount of heat at the ends of the kiln is produced.

19. In a dry kiln, in combination a return coil heating system, distributed within the kiln, a distributed fan system for circulating atmosphere transversely across said heating system within the kiln, said fan system comprising a series of fans operatively mounted at intervals and rotated at substantially the same speed within the kiln, the fans adjacent to the ends of the kiln being of greater capacity than the intermediate fans, substantially as and for the purpose specified.

20. In a dry kiln, the combination with heating and humidifying means distributed therein, means for effecting substantially transverse air circulation therein substantially the full length of the kiln across said heating and humidifying means, effective substantially the full length of the kiln, said heating and humidifying means at one end of the kiln providing more heat at that end of the kiln than at the other portions thereof.

21. In a dry kiln having a series of fans operatively mounted and distributed in substantial alignment therein, the combination of a return coil heating system comprising top and bottom headers, and top and bottom legs connected, respectively, thereto, said headers being vertically spaced apart at one end of said heating system, said legs converging and being connected by a return joint at its opposite end, said headers being supplied with steam and drained respectively, said heating system being so related to said fans that a greater volume of air is circulated across the upper leg than across the lower leg of said heating system, and across extended surface radiation, provided on said heating system adjacent to one of the ends of the kiln.

JAMES FORREST COBB. 

